George Gamow (1946) - Proposed
the "hot" model for creation of the universe. This hot explosion
would have been expected to produce a background radiation temperature of
5°K (Kelvin is a metric scale of temperature, with absolute zero, the
lowest possible temperature, at which no molecular motion occurs, equal to
zero). At the time there was no known way to measure a temperature this
low from earth, so there was no way to test this theory.

Bell Labs (1965) - Scientists at
Bell Labs were measuring radio emission at 7 cm wavelength (where emission
from galaxies was negligible) and found a 3°K excess in antenna
temperature. This 3°K background temperature was found throughout the
entire universe.